It's easy, really :3
Just go to
www.imageshack.us
Then you should see a button that says browse, and you click it. It will prompt you to find the file located on your computer (I usually temporarily save the file I wish to upload on my desktop, so it's easy to find), one you find the file, double click it, and the located should appear in the bar to the left of the browse button.
Then hit upload, and it will upload the image for you, and just copy and paste the url, and post it here =)
It's also free, so you don't need to worry about fees of any kind =)